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Ashton AW. Preparing to strike: Acute events in signaling by the serpentine receptor for thromboxane A 2. Pharmacol Ther 2023:108478. [PMID: 37321373 DOI: 10.1016/j.pharmthera.2023.108478] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Revised: 05/31/2023] [Accepted: 06/07/2023] [Indexed: 06/17/2023]
Abstract
Over the last two decades, awareness of the (patho)physiological roles of thromboxane A2 signaling has been greatly extended. From humble beginnings as a short-lived stimulus that activates platelets and causes vasoconstriction to a dichotomous receptor system involving multiple endogenous ligands capable of modifying tissue homeostasis and disease generation in almost every tissue of the body. Thromboxane A2 receptor (TP) signal transduction is associated with the pathogenesis of cancer, atherosclerosis, heart disease, asthma, and host response to parasitic infection amongst others. The two receptors mediating these cellular responses (TPα and TPβ) are derived from a single gene (TBXA2R) through alternative splicing. Recently, knowledge about the mechanism(s) of signal propagation by the two receptors has undergone a revolution in understanding. Not only have the structural relationships associated with G-protein coupling been established but the modulation of that signaling by post-translational modification to the receptor has come sharply into focus. Moreover, the signaling of the receptor unrelated to G-protein coupling has become a burgeoning field of endeavor with over 70 interacting proteins currently identified. These data are reshaping the concept of TP signaling from a mere guanine nucleotide exchange factors for Gα activation to a nexus for the convergence of diverse and poorly characterized signaling pathways. This review summarizes the advances in understanding in TP signaling, and the potential for new growth in a field that after almost 50 years is finally coming of age.
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Affiliation(s)
- Anthony W Ashton
- Division of Cardiovascular Medicine, Lankenau Institute for Medical Research, Rm 128, 100 E Lancaster Ave, Wynnewood, PA 19096, USA; Division of Perinatal Research, Kolling Institute of Medical Research, Faculty of Medicine and Health, University of Sydney, St Leonards, NSW 2065, Australia.
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2
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Gui X, Chu X, Du Y, Wang Y, Zhang S, Ding Y, Tong H, Xu M, Li Y, Ju W, Sun Z, Li Z, Zeng L, Xu K, Qiao J. Impaired Platelet Function and Thrombus Formation in PDE5A-Deficient Mice. Thromb Haemost 2023; 123:207-218. [PMID: 36252813 DOI: 10.1055/a-1962-1613] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Intracellular cyclic GMP (cGMP) inhibits platelet function. Platelet cGMP levels are controlled by phosphodiesterase 5A (PDE5A)-mediated degradation. However, the exact role of PDE5A in platelet function and thrombus formation remains poorly understood. In this study, we characterized the role of PDE5A in platelet activation and function. Platelets were isolated from wild type or PDE5A-/- mice to measure platelet aggregation, activation, phosphatidylserine exposure (annexin-V binding), reactive oxygen species (ROS) generation, platelet spreading as well as clot retraction. Cytosolic calcium mobilization was measured using Fluo-4 AM by a microplate reader. Western blot was used to measure the phosphorylation of VASP, ERK1/2, p38, JNK, and AKT. FeCl3-induced arterial thrombosis and venous thrombosis were assessed to evaluate the in vivo hemostatic function and thrombus formation. Additionally, in vitro thrombus formation was assessed in a microfluidic whole-blood perfusion assay. PDE5A-deficient mice presented significantly prolonged tail bleeding time and delayed arterial and venous thrombus formation. PDE5A deficiency significantly inhibited platelet aggregation, ATP release, P-selectin expression, and integrin aIIbb3 activation. In addition, an impaired spreading on collagen or fibrinogen and clot retraction was observed in PDE5A-deficient platelets. Moreover, PDE5A deficiency reduced phosphatidylserine exposure, calcium mobilization, ROS production, and increased intracellular cGMP level along with elevated VASP phosphorylation and reduced phosphorylation of ERK1/2, p38, JNK, and AKT. In conclusion, PDE5A modulates platelet activation and function and thrombus formation, indicating that therapeutically targeting it might be beneficial for the treatment of thrombotic diseases.
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Affiliation(s)
- Xiang Gui
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Xiang Chu
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Yuwei Du
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Yuhan Wang
- School of Medical Technology, Xuzhou Medical University, Xuzhou, People's Republic of China
| | - Sixuan Zhang
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Yangyang Ding
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Huan Tong
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Mengdi Xu
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Yue Li
- School of Medical Technology, Xuzhou Medical University, Xuzhou, People's Republic of China
| | - Wen Ju
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Zengtian Sun
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Zhenyu Li
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Lingyu Zeng
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China.,School of Medical Technology, Xuzhou Medical University, Xuzhou, People's Republic of China
| | - Kailin Xu
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
| | - Jianlin Qiao
- Blood Diseases Institute, Xuzhou Medical University, Xuzhou, People's Republic of China.,Department of Hematology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, People's Republic of China.,Key Laboratory of Bone Marrow Stem Cell, Jiangsu Province, Xuzhou, People's Republic of China
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3
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Biringer RG. A Review of Prostanoid Receptors: Expression, Characterization, Regulation, and Mechanism of Action. J Cell Commun Signal 2020; 15:155-184. [PMID: 32970276 DOI: 10.1007/s12079-020-00585-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2020] [Accepted: 09/15/2020] [Indexed: 12/22/2022] Open
Abstract
Prostaglandin signaling controls a wide range of biological processes from blood pressure homeostasis to inflammation and resolution thereof to the perception of pain to cell survival. Disruption of normal prostanoid signaling is implicated in numerous disease states. Prostaglandin signaling is facilitated by G-protein-coupled, prostanoid-specific receptors and the array of associated G-proteins. This review focuses on the expression, characterization, regulation, and mechanism of action of prostanoid receptors with particular emphasis on human isoforms.
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Affiliation(s)
- Roger G Biringer
- College of Osteopathic Medicine, Lake Erie College of Osteopathic Medicine, 5000 Lakewood Ranch Blvd, Bradenton, FL, 34211, USA.
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5
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Prostacyclin reverses platelet stress fibre formation causing platelet aggregate instability. Sci Rep 2017; 7:5582. [PMID: 28717253 PMCID: PMC5514131 DOI: 10.1038/s41598-017-05817-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Accepted: 06/02/2017] [Indexed: 01/10/2023] Open
Abstract
Prostacyclin (PGI2) modulates platelet activation to regulate haemostasis. Evidence has emerged to suggest that thrombi are dynamic structures with distinct areas of differing platelet activation. It was hypothesised that PGI2 could reverse platelet spreading by actin cytoskeletal modulation, leading to reduced capability of platelet aggregates to withstand a high shear environment. Our data demonstrates that post-flow of PGI2 over activated and spread platelets on fibrinogen, identified a significant reduction in platelet surface area under high shear. Exploration of the molecular mechanisms underpinning this effect revealed that PGI2 reversed stress fibre formation in adherent platelets, reduced platelet spreading, whilst simultaneously promoting actin nodule formation. The effects of PGI2 on stress fibres were mimicked by the adenylyl cyclase activator forskolin and prevented by inhibitors of protein kinase A (PKA). Stress fibre formation is a RhoA dependent process and we found that treatment of adherent platelets with PGI2 caused inhibitory phosphorylation of RhoA, reduced RhoA GTP-loading and reversal of myosin light chain phosphorylation. Phospho-RhoA was localised in actin nodules with PKA type II and a number of other phosphorylated PKA substrates. This study demonstrates that PGI2 can reverse key platelet functions after their initial activation and identifies a novel mechanism for controlling thrombosis.
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Unsworth AJ, Kriek N, Bye AP, Naran K, Sage T, Flora GD, Gibbins JM. PPARγ agonists negatively regulate αIIbβ3 integrin outside-in signaling and platelet function through up-regulation of protein kinase A activity. J Thromb Haemost 2017; 15:356-369. [PMID: 27896950 PMCID: PMC5396324 DOI: 10.1111/jth.13578] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Indexed: 12/31/2022]
Abstract
Essentials peroxisome proliferator-activated receptor γ (PPARγ) agonists inhibit platelet function. PPARγ agonists negatively regulate outside-in signaling via integrin αIIbβ3. PPARγ agonists disrupt the interaction of Gα13 with integrin β3. This is attributed to an upregulation of protein kinase A activity. SUMMARY Background Agonists for the peroxisome proliferator-activated receptor (PPARγ) have been shown to have inhibitory effects on platelet activity following stimulation by GPVI and GPCR agonists. Objectives Profound effects on thrombus formation led us to suspect a role for PPARγ agonists in the regulation of integrin αIIbβ3 mediated signaling. Both GPVI and GPCR signaling pathways lead to αIIbβ3 activation, and signaling through αIIbβ3 plays a critical role in platelet function and normal hemostasis. Methods The effects of PPARγ agonists on the regulation of αIIbβ3 outside-in signaling was determined by monitoring the ability of platelets to adhere and spread on fibrinogen and undergo clot retraction. Effects on signaling components downstream of αIIbβ3 activation were also determined following adhesion to fibrinogen by Western blotting. Results Treatment of platelets with PPARγ agonists inhibited platelet adhesion and spreading on fibrinogen and diminished clot retraction. A reduction in phosphorylation of several components of αIIbβ3 signaling, including the integrin β3 subunit, Syk, PLCγ2, focal adhesion kinase (FAK) and Akt, was also observed as a result of reduced interaction of the integrin β3 subunit with Gα13. Studies of VASP phosphorylation revealed that this was because of an increase in PKA activity following treatment with PPARγ receptor agonists. Conclusions This study provides further evidence for antiplatelet actions of PPARγ agonists, identifies a negative regulatory role for PPARγ agonists in the control of integrin αIIbβ3 outside-in signaling, and provides a molecular basis by which the PPARγ agonists negatively regulate platelet activation and thrombus formation.
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Affiliation(s)
- A. J. Unsworth
- Institute for Cardiovascular and Metabolic ResearchSchool of Biological SciencesUniversity of ReadingReadingUK
| | - N. Kriek
- Institute for Cardiovascular and Metabolic ResearchSchool of Biological SciencesUniversity of ReadingReadingUK
| | - A. P. Bye
- Institute for Cardiovascular and Metabolic ResearchSchool of Biological SciencesUniversity of ReadingReadingUK
| | - K. Naran
- Institute for Cardiovascular and Metabolic ResearchSchool of Biological SciencesUniversity of ReadingReadingUK
| | - T. Sage
- Institute for Cardiovascular and Metabolic ResearchSchool of Biological SciencesUniversity of ReadingReadingUK
| | - G. D. Flora
- Institute for Cardiovascular and Metabolic ResearchSchool of Biological SciencesUniversity of ReadingReadingUK
| | - J. M. Gibbins
- Institute for Cardiovascular and Metabolic ResearchSchool of Biological SciencesUniversity of ReadingReadingUK
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7
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Unsworth AJ, Bye AP, Gibbins JM. Platelet-Derived Inhibitors of Platelet Activation. PLATELETS IN THROMBOTIC AND NON-THROMBOTIC DISORDERS 2017. [PMCID: PMC7123044 DOI: 10.1007/978-3-319-47462-5_37] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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8
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Krappmann M, de Boer AR, Kool DRW, Irth H, Letzel T. Mass spectrometric real-time monitoring of an enzymatic phosphorylation assay using internal standards and data-handling freeware. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2016; 30:1019-1030. [PMID: 27003039 DOI: 10.1002/rcm.7529] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Revised: 02/01/2016] [Accepted: 02/02/2016] [Indexed: 06/05/2023]
Abstract
RATIONALE Continuous-flow reaction detection systems (monitoring enzymatic reactions with mass spectrometry (MS)) lack quantitative values so far. Therefore, two independent internal standards (IS) are implemented in a way that the online system stability can be observed, quantitative conversion values for substrate and product can be obtained and they can be used as mass calibration standards for high MS accuracy. METHODS An application previously developed for the MS detection of peptide phosphorylation by cAMP-dependent protein kinase A (PKA) (De Boer et al., Anal. Bioanal. Chem. 2005, 381, 647-655) was transferred to a continuous-flow reaction detection system. This enzymatic reaction, involving enzyme activation as well as the transfer of a phosphate group from ATP to a peptide substrate, was used to prove the compatibility of a quantitative enzymatic assay in a continuous-flow real-time system (connected to MS). RESULTS Moreover (using internal standards), the critical parameter reaction temperature (including solution density variations depending on temperature) was studied in the continuous-flow mixing system. Furthermore, two substrates (malantide and kemptide), two enzyme types (catalytic subunit of PKA and complete PKA) and one inhibitor were tested to determine system robustness and long-term availability. Even spraying solutions that contained significant amount of MS contaminants (e.g. the polluted catalytic subunit) resulted in quantifiable MS signal intensities. Subsequent recalculations using the internal standards led to results representing the power of this application. CONCLUSIONS The presented methodology and the data evaluation with available Achroma freeware enable the direct coupling of biochemical assays with quantitative MS detection. Monitoring changes such as temperature, reaction time, inhibition, or compound concentrations can be observed quantitatively and thus enzymatic activity can be calculated.
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Affiliation(s)
- Michael Krappmann
- Zentrum für Forschung und Weiterbildung, Weihenstephan-Triesdorf - University of Applied Science, Am Staudengarten 7, D-85354, Freising-Weihenstephan, Germany
| | - Arjen R de Boer
- Faculty of Sciences, Division of Chemistry, Department of Analytical Chemistry and Applied Spectroscopy, Free University of Amsterdam, De Boelelaan 1083, NL-1081 HV, Amsterdam, The Netherlands
| | - Daniël R W Kool
- Faculty of Sciences, Division of Chemistry, Department of Analytical Chemistry and Applied Spectroscopy, Free University of Amsterdam, De Boelelaan 1083, NL-1081 HV, Amsterdam, The Netherlands
| | - Hubertus Irth
- Faculty of Sciences, Division of Chemistry, Department of Analytical Chemistry and Applied Spectroscopy, Free University of Amsterdam, De Boelelaan 1083, NL-1081 HV, Amsterdam, The Netherlands
| | - Thomas Letzel
- Faculty of Sciences, Division of Chemistry, Department of Analytical Chemistry and Applied Spectroscopy, Free University of Amsterdam, De Boelelaan 1083, NL-1081 HV, Amsterdam, The Netherlands
- Analytical Research Group, Chair of Urban Water Systems Engineering, Technical University of Munich, Am Coulombwall 8, D-85748, Garching, Germany
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Budnik I, Shenkman B, Savion N. Role of G protein signaling in the formation of the fibrin(ogen)–integrin αIIbβ3–actin cytoskeleton complex in platelets. Platelets 2016; 27:563-75. [DOI: 10.3109/09537104.2016.1147544] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Affiliation(s)
- Ivan Budnik
- Goldschleger Eye Research Institute and the Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
- Department of Pathophysiology, Sechenov First Moscow State Medical University, Moscow, Russia
| | - Boris Shenkman
- National Hemophilia Center, Sheba Medical Center, Tel-Hashomer, Israel
| | - Naphtali Savion
- Goldschleger Eye Research Institute and the Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
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Abstract
MLCP (myosin light chain phosphatase) regulates platelet function through its ability to control myosin IIa phosphorylation. Recent evidence suggests that MLCP is a de facto target for signalling events stimulated by cAMP. In the present mini-review, we discuss the mechanisms by which cAMP signalling maintains MLCP in an active state to control platelet contractile machinery.
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cAMP signaling regulates platelet myosin light chain (MLC) phosphorylation and shape change through targeting the RhoA-Rho kinase-MLC phosphatase signaling pathway. Blood 2013; 122:3533-45. [PMID: 24100445 DOI: 10.1182/blood-2013-03-487850] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Cyclic adenosine monophosphate (cAMP)-dependent signaling modulates platelet shape change through unknown mechanisms. We examined the effects of cAMP signaling on platelet contractile machinery. Prostaglandin E1 (PGE1)-mediated inhibition of thrombin-stimulated shape change was accompanied by diminished phosphorylation of myosin light chain (MLC). Since thrombin stimulates phospho-MLC through RhoA/Rho-associated, coiled-coil containing protein kinase (ROCK)-dependent inhibition of MLC phosphatase (MLCP), we examined the effects of cAMP on this pathway. Thrombin stimulated the membrane localization of RhoA and the formation of a signaling complex of RhoA/ROCK2/myosin phosphatase-targeting subunit 1 (MYPT1). This resulted in ROCK-mediated phosphorylation of MYPT1 on threonine 853 (thr(853)), the disassociation of the catalytic subunit protein phosphatase 1δ (PP1δ) from MYPT1 and inhibition of basal MLCP activity. Treatment of platelets with PGE1 prevented thrombin-induced phospho-MYPT1-thr(853) in a protein kinase A (PKA)-dependent manner. Examination of the molecular mechanisms revealed that PGE1 induced the phosphorylation of RhoA on serine(188) through a pathway requiring cAMP and PKA. This event inhibited the membrane relocalization of RhoA, prevented the association of RhoA with ROCK2 and MYPT1, attenuated the dissociation of PP1δ from MYPT1, and thereby restored basal MLCP activity leading to a decrease in phospho-MLC. These data reveal a new mechanism by which the cAMP-PKA signaling pathway regulates platelet function.
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Abstract
Endothelial prostacyclin and nitric oxide potently inhibit platelet functions. Prostacyclin and nitric oxide actions are mediated by platelet adenylyl and guanylyl cyclases, which synthesize cyclic AMP (cAMP) and cyclic GMP (cGMP), respectively. Cyclic nucleotides stimulate cAMP-dependent protein kinase (protein kinase A [PKA]I and PKAII) and cGMP-dependent protein kinase (protein kinase G [PKG]I) to phosphorylate a broad panel of substrate proteins. Substrate phosphorylation results in the inactivation of small G-proteins of the Ras and Rho families, inhibition of the release of Ca(2+) from intracellular stores, and modulation of actin cytoskeleton dynamics. Thus, PKA/PKG substrates translate prostacyclin and nitric oxide signals into a block of platelet adhesion, granule release, and aggregation. cAMP and cGMP are degraded by phosphodiesterases, which might restrict signaling to specific subcellular compartments. An emerging principle of cyclic nucleotide signaling in platelets is the high degree of interconnection between activating and cAMP/cGMP-dependent inhibitory signaling pathways at all levels, including cAMP/cGMP synthesis and breakdown, and PKA/PKG-mediated substrate phosphorylation. Furthermore, defects in cAMP/cGMP pathways might contribute to platelet hyperreactivity in cardiovascular disease. This article focuses on recent insights into the regulation of the cAMP/cGMP signaling network and on new targets of PKA and PKG in platelets.
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Affiliation(s)
- A Smolenski
- UCD Conway Institute, UCD School of Medicine and Medical Science, University College Dublin, Belfield, Dublin, Ireland.
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Broos K, Feys HB, De Meyer SF, Vanhoorelbeke K, Deckmyn H. Platelets at work in primary hemostasis. Blood Rev 2011; 25:155-67. [PMID: 21496978 DOI: 10.1016/j.blre.2011.03.002] [Citation(s) in RCA: 283] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
When platelet numbers are low or when their function is disabled, the risk of bleeding is high, which on the one hand indicates that in normal life vascular damage is a rather common event and that hence the role of platelets in maintaining a normal hemostasis is a continuously ongoing physiological process. Upon vascular injury, platelets instantly adhere to the exposed extracellular matrix resulting in platelet activation and aggregation to form a hemostatic plug. This self-amplifying mechanism nevertheless requires a tight control to prevent uncontrolled platelet aggregate formation that eventually would occlude the vessel. Therefore endothelial cells produce inhibitory compounds such as prostacyclin and nitric oxide that limit the growth of the platelet thrombus to the damaged area. With this review, we intend to give an integrated survey of the platelet response to vascular injury in normal hemostasis.
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Affiliation(s)
- Katleen Broos
- Laboratory for Thrombosis Research, IRF Life Sciences, KU Leuven Campus Kortrijk, Belgium.
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Walter U, Gambaryan S. cGMP and cGMP-dependent protein kinase in platelets and blood cells. Handb Exp Pharmacol 2009:533-48. [PMID: 19089344 DOI: 10.1007/978-3-540-68964-5_23] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Platelets are specialized adhesive cells that play a key role in normal and pathological hemostasis through their ability to rapidly adhere to subendothelial matrix proteins (platelet adhesion) and to other activated platelets (platelet aggregation). NO plays a crucial role in preventing platelet adhesion and aggregation. In platelets, cGMP synthesis is catalyzed by sGC, whereas PDE2, PDE3 and PDE5 are responsible for cGMP degradation. Stimulation of cGK by cGMP leads to phosphorylation of multiple target substrates. These substrates inhibit elevation of intracellular calcium, integrin activation, cytoskeletal reorganization, and platelet granule secretion, events normally associated with platelet activation. The NO/cGMP pathway also plays a significant role in many other blood cell types in addition to platelets. In leukocytes, depending on the specific cell type, cGMP signaling regulates gene expression, differentiation, migration, cytokine production, and apoptosis.
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Affiliation(s)
- Ulrich Walter
- Institute of Clinical Biochemistry and Pathobiochemistry, University of Wuerzburg, Josef-Schneider-Str. 2, Wuerzburg, 97080, Germany.
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The critical roles of cyclic AMP/cyclic AMP-dependent protein kinase in platelet physiology. ACTA ACUST UNITED AC 2008. [DOI: 10.1007/s11515-008-0098-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Lundblad C, Grände PO, Bentzer P. Increased cortical cell loss and prolonged hemodynamic depression after traumatic brain injury in mice lacking the IP receptor for prostacyclin. J Cereb Blood Flow Metab 2008; 28:367-76. [PMID: 17713464 DOI: 10.1038/sj.jcbfm.9600533] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Prostacyclin is the major arachidonic acid metabolite of the vascular endothelium and is produced mainly via the cyclooxygenase-2 pathway. By acting on the prostacyclin (IP) receptor on platelets and vascular smooth muscle cells, prostacyclin exerts vasodilatory and antiaggregative/antiadhesive effects. Previous studies have shown that prostacyclin production increases after brain trauma, but the importance of prostacyclin for posttraumatic hemodynamic alterations and neuron survival has not been investigated. This study evaluated if endogenous prostacyclin plays a role in the pathophysiologic process in the brain after brain trauma. This was performed by comparing prostacyclin (IP) receptor-deficient (IP(-/-)) mice and mice with functional IP receptor (IP(+/+)) after a controlled cortical injury regarding contusion volume, cerebral blood flow ([(14)C]iodoantipyrine autoradiography), number of perfused capillaries (fluorescein isothiocyanate-dextran fluorescence technique), the transfer constant (K(i)) for [(51)Cr]EDTA, and brain water content (wet vs dry weight) in the injured and contralateral cortex. Contusion volume was increased in IP(-/-) mice compared with IP(+/+) mice. Three hours after trauma, cortical blood flow was decreased in the injured cortex of both groups and the reduction in blood flow in the cortex of the IP(-/-) mice persisted from 3 to 24 h, whereas blood flow approached normal values in the IP(+/+) mice after 24 h. No differences could be detected between the two genotypes regarding other hemodynamic parameters. We conclude that the prostacyclin IP receptor is beneficial for neuron survival after brain trauma in mice, an effect that may be mediated by improved cortical perfusion.
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Affiliation(s)
- Cornelia Lundblad
- Department of Anesthesiology and Intensive Care, University of Lund and Lund University Hospital, Lund, Sweden
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Huang JS, Dong L, Kozasa T, Le Breton GC. Signaling through G(alpha)13 switch region I is essential for protease-activated receptor 1-mediated human platelet shape change, aggregation, and secretion. J Biol Chem 2007; 282:10210-22. [PMID: 17298951 DOI: 10.1074/jbc.m605678200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
This study investigated the involvement of Galpha(13) switch region I (SRI) in protease-activated receptor 1 (PAR1)-mediated platelet function and signaling. To this end, myristoylated peptides representing the Galpha(13) SRI (Myr-G(13)SRI(pep)) and its random counterpart were evaluated for their effects on PAR1 activation. Initial studies demonstrated that Myr-G(13)SRI(pep) and Myr-G(13)SRI(Random-pep) were equally taken up by human platelets and did not interfere with PAR1-ligand interaction. Subsequent experiments revealed that Myr-G(13)SRI(pep) specifically bound to platelet RhoA guanine nucleotide exchange factor (p115RhoGEF) and blocked PAR1-mediated RhoA activation in platelets and human embryonic kidney cells. These results suggest a direct interaction of Galpha(13) SRI with p115RhoGEF and a mechanism for Myr-G(13)SRI(pep) inhibition of RhoA activation. Platelet function studies demonstrated that Myr-G(13)SRI(pep) specifically inhibited PAR1-stimulated shape change, aggregation, and secretion in a dose-dependent manner but did not inhibit platelet activation induced by either ADP or A23187. It was also found that Myr-G(13)SRI(pep) inhibited low dose, but not high dose, thrombin-induced aggregation. Additional experiments showed that PAR1-mediated calcium mobilization was partially blocked by Myr-G(13)SRI(pep) but not by the Rho kinase inhibitor Y-27632. Finally, Myr-G(13)SRI(pep) effectively inhibited PAR1-induced stress fiber formation and cell contraction in endothelial cells. Collectively, these results suggest the following: 1) interaction of Galpha(13) SRI with p115RhoGEF is required for G(13)-mediated RhoA activation in platelets; 2) signaling through the G(13) pathway is critical for PAR1-mediated human platelet functional changes and low dose thrombin-induced aggregation; and 3) G(13) signaling elicits calcium mobilization in human platelets through a Rho kinase-independent mechanism.
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Affiliation(s)
- Jin-Sheng Huang
- Department of Pharmacology, College of Medicine University of Illinois at Chicago, Chicago, Illinois 60612
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18
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19
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Abstract
Phosphorylation of Ser19 on the 20-kDa regulatory light chain of myosin II (MLC20) by Ca2+/calmodulin-dependent myosin light-chain kinase (MLCK) is essential for initiation of smooth muscle contraction. The initial [Ca2+]i transient is rapidly dissipated and MLCK inactivated, whereas MLC20 and muscle contraction are well maintained. Sustained contraction does not reflect Ca2+ sensitization because complete inhibition of MLC phosphatase activity in the absence of Ca2+ induces smooth muscle contraction. This contraction is suppressed by staurosporine, implying participation of a Ca2+-independent MLCK. Thus, sustained contraction, as with agonist-induced contraction at experimentally fixed Ca2+ concentrations, involves (a) G protein activation, (b) regulated inhibition of MLC phosphatase, and (c) MLC20 phosphorylation via a Ca2+-independent MLCK. The pathways that lead to inhibition of MLC phosphatase by G(q/13)-coupled receptors are initiated by sequential activation of Galpha(q)/alpha13, RhoGEF, and RhoA, and involve Rho kinase-mediated phosphorylation of the regulatory subunit of MLC phosphatase (MYPT1) and/or PKC-mediated phosphorylation of CPI-17, an endogenous inhibitor of MLC phosphatase. Sustained MLC20 phosphorylation is probably induced by the Ca2+-independent MLCK, ZIP kinase. The pathways initiated by G(i)-coupled receptors involve sequential activation of Gbetagamma(i), PI 3-kinase, and the Ca2+-independent MLCK, integrin-linked kinase. The last phosphorylates MLC20 directly and inhibits MLC phosphatase by phosphorylating CPI-17. PKA and PKG, which mediate relaxation, act upstream to desensitize the receptors (VPAC2 and NPR-C), inhibit adenylyl and guanylyl cyclase activities, and stimulate cAMP-specific PDE3 and PDE4 and cGMP-specific PDE5 activities. These kinases also act downstream to inhibit (a) initial contraction by inhibiting Ca2+ mobilization and (b) sustained contraction by inhibiting RhoA and targets downstream of RhoA. This increases MLC phosphatase activity and induces MLC20 dephosphorylation and muscle relaxation.
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Affiliation(s)
- Karnam S Murthy
- Department of Physiology, Virginia Commonwealth University Medical Center, Richmond, Virginia 23298, USA.
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20
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Huang JS, Dong L, Le Breton GC. Mass-dependent signaling between G protein coupled receptors. Cell Signal 2006; 18:564-76. [PMID: 16125366 DOI: 10.1016/j.cellsig.2005.06.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2005] [Accepted: 06/10/2005] [Indexed: 12/14/2022]
Abstract
The present study provides evidence that G protein coupled receptor (GPCR) signaling pathways participate in an interactive signaling network governed by the principles of mass action. Using an inducible thromboxane A2 receptor (TPR)/platelet activating factor receptor (PAFR) co-expressing cell model, TPR or PAFR expression was independently up-regulated. Immunostaining and radioligand binding experiments demonstrated that this receptor up-regulation resulted in increased GPCR:G protein mass ratios. This increase in mass ratio impacted both TPR and PAFR ligand affinity. Specifically, up-regulating TPR expression not only decreased TPR ligand affinity, but also decreased the ligand affinity of PAFRs. A similar effect on ligand affinities was observed when PAFRs were up-regulated. In addition, increasing the GPCR:G protein mass ratio for TPRs led to desensitization of the calcium mobilization response to PAFR activation, and increasing PAFR mass desensitized the TPR-mediated calcium response. Finally, it was observed that an increased TPR:G protein mass ratio was associated with a shift in the TPR signaling response, and revealed an additional TPR signaling pathway through G(S). Collectively, these results describe a novel mechanism, i.e., mass-dependent GPCR signaling, by which cells can modulate their GPCR signaling pathways and signaling priorities.
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MESH Headings
- 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid/pharmacology
- Animals
- Azepines/pharmacology
- Blood Platelets/drug effects
- CHO Cells
- Calcium/metabolism
- Cricetinae
- Humans
- Ligands
- Platelet Membrane Glycoproteins/antagonists & inhibitors
- Platelet Membrane Glycoproteins/metabolism
- Receptors, G-Protein-Coupled/antagonists & inhibitors
- Receptors, G-Protein-Coupled/drug effects
- Receptors, G-Protein-Coupled/metabolism
- Receptors, Thromboxane A2, Prostaglandin H2/agonists
- Receptors, Thromboxane A2, Prostaglandin H2/antagonists & inhibitors
- Receptors, Thromboxane A2, Prostaglandin H2/metabolism
- Signal Transduction/drug effects
- Signal Transduction/physiology
- Time Factors
- Triazoles/pharmacology
- Up-Regulation
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Affiliation(s)
- Jin-Sheng Huang
- Department of Pharmacology, College of Medicine, University of Illinois at Chicago, 835 S. Wolcott Ave. (mail code 868), Chicago, IL 60612, USA
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21
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Russo I, Doronzo G, Mattiello L, De Salve A, Trovati M, Anfossi G. The activity of constitutive nitric oxide synthase is increased by the pathway cAMP/cAMP-activated protein kinase in human platelets. New insights into the antiaggregating effects of cAMP-elevating agents. Thromb Res 2005; 114:265-73. [PMID: 15381390 DOI: 10.1016/j.thromres.2004.06.036] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2004] [Revised: 06/04/2004] [Accepted: 06/17/2004] [Indexed: 10/26/2022]
Abstract
Human platelets synthesize nitric oxide (NO) through an endothelial-type NO synthase (ecNOS) activated also by substances enhancing 3',5'-cyclic adenosine monophosphate (cAMP) concentrations, such as catecholamines, beta-adrenoceptor agonists and adenosine. To verify whether cAMP directly activates ecNOS through the cAMP-dependent protein kinase A (PKA), we evaluated (i) the influence of 8-Br-cAMP, adenosine and forskolin on ecNOS activity and phosphorylation at Ser(1177) and (ii) the effect of PKA inhibition on ecNOS activity. Platelets from 10 healthy male volunteers were used for aggregation studies and measurement of NOS activity (conversion of L-[(3)H]-arginine to L-[(3)H]-citrulline) following exposure to 8-Br-cAMP, adenosine and forskolin, both in the absence and in the presence of the PKA inhibitor Rp-cAMPS (100 micromol/l). The phosphorylation of the PKA substrate vasodilator-stimulated phosphoprotein (VASP) at Ser(157) and Ser(239) and of ecNOS at Ser(1177) was evaluated by Western blot. NOS activity (pmol L-citrulline/10(8) platelets) increased from 0.090+/-0.002 to 0.148+/-0.013 with 500 micromol/l 8-Br-cAMP (p<0.0001), to 0.140+/-0.008 with 30 micromol/l adenosine (p<0.0001) and to 0.140+/-0.009 with 10 micromol/l forskolin (p<0.0001). Rp-cAMPS decreased baseline NOS activity from 0.093+/-0.001 to 0.075+/-0.006 (p<0.02) and prevented the stimulation by 8-Br-cAMP, adenosine and forskolin. Platelet exposure to 8-Br-cAMP and forskolin, beside the phosphorylation of the specific PKA substrate VASP, markedly increased the expression of ecNOS protein phosphorylated at Ser(1177). The study shows that NOS activity of human platelets is increased by the cAMP/PKA pathway which is involved in NO synthesis induced by adenosine, forskolin and potentially by every antiaggregating substance enhancing intraplatelet cAMP via receptor-dependent and -independent mechanisms.
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Affiliation(s)
- Isabella Russo
- Diabetes Unit, Department of Clinical and Biological Sciences of the Turin University, Ospedale San Luigi Gonzaga Hospital, Regione Gonzole, 10, Orbassano 10043, Turin, Italy
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22
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Reid HM, Kinsella BT. The α, but Not the β, Isoform of the Human Thromboxane A2 Receptor Is a Target for Nitric Oxide-mediated Desensitization. J Biol Chem 2003; 278:51190-202. [PMID: 14530262 DOI: 10.1074/jbc.m309314200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In humans, thromboxane A2 signals through two thromboxane A2 receptor (TP) isoforms termed TP alpha and TP beta. Signaling by TP alpha, but not TP beta, is subject to prostacyclin-induced desensitization mediated by direct protein kinase (PK) A phosphorylation where Ser329 represents the phosphotarget (Walsh, M. T., Foley, J. F., and Kinsella, B. T. (2000) J. Biol. Chem. 275, 20412-20423). In the current study, the effect of the vasodilator nitric oxide (NO) on intracellular signaling by the TP isoforms was investigated. The NO donor 3-morpholinosydnonimine, HCl (SIN-1) and 8-bromo-guanosine 3',5'-cyclic monophosphate (8-Br-cGMP) functionally desensitized U46619-mediated calcium mobilization and inositol 1,4,5-trisphosphate generation by TP alpha whereas signaling by TP beta was unaffected by either agent. NO-mediated desensitization of TP alpha signaling occurred through a PKG-dependent, PKA- and PKC-independent mechanism. TP alpha, but not TP beta, was efficiently phosphorylated by PKG in vitro and underwent NO/PKG-mediated phosphorylation in whole cells. Deletion/site-directed mutagenesis and metabolic labeling studies identified Ser331 as the target residue of NO-induced PKG phosphorylation of TP alpha. Although TP alpha S331A was insensitive to NO/PKG-desensitization, similar to wild type TP alpha its signaling was fully desensitized by the prostacyclin receptor agonist cicaprost occurring through a PKA-dependent mechanism. Conversely, signaling by TP alpha S329A was insensitive to cicaprost stimulation whereas it was fully desensitized by NO/PKG signaling. In conclusion, TP alpha undergoes both NO- and prostacyclin-mediated desensitization that occur through entirely independent mechanisms involving direct PKG phosphorylation of Ser331, in response to NO, and PKA phosphorylation of Ser329, in response to prostacyclin, within the unique carboxyl-terminal tail domain of TP alpha. On the other hand, signaling by TP beta is unaffected by either NO or prostacyclin.
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Affiliation(s)
- Helen M Reid
- Department of Biochemistry, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
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23
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Sim DS, Merrill-Skoloff G, Furie BC, Furie B, Flaumenhaft R. Initial accumulation of platelets during arterial thrombus formation in vivo is inhibited by elevation of basal cAMP levels. Blood 2003; 103:2127-34. [PMID: 14645013 DOI: 10.1182/blood-2003-04-1133] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Platelet accumulation at sites of vascular injury is the primary event in arterial thrombosis. Initial platelet accrual into thrombi is mediated by interactions of platelet adhesion receptors with ligands on the injured endothelium or in the sub-endothelial matrix. The role of intracellular signals in initial platelet accumulation at sites of endothelial injury, however, is the subject of debate. We have used a newly discovered inhibitor of phosphodiesterase 3A (PDE3A) and the well-characterized PDE3A inhibitor, cilostazol, to modulate 3',5'-cyclic adenosine monophosphate (cAMP) levels in an in vivo model that enables the kinetic analysis of platelet accumulation. These studies demonstrate that elevation of basal cAMP levels results in an overall decline in platelet accumulation at the site of vascular injury. In particular, the initial rate of accumulation of platelets is inhibited by elevation of cAMP. Analysis of the kinetics of individual platelets at injury sites using intravital microscopy demonstrates that cAMP directs the rate at which platelets attach to and detach from thrombi. These studies demonstrate that cAMP in circulating platelets controls attachment to and detachment from sites of arteriolar injury. Thus, the status of the intracellular signaling machinery prior to engagement of platelet receptors influences the rate of platelet accumulation during thrombus formation.
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Affiliation(s)
- Derek S Sim
- Center for Hemostasis and Thrombosis Research, Beth Israel Deaconess Medical Center, 41 Ave Louis Pasteur, Boston, MA 02115, USA
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24
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Moers A, Nieswandt B, Massberg S, Wettschureck N, Grüner S, Konrad I, Schulte V, Aktas B, Gratacap MP, Simon MI, Gawaz M, Offermanns S. G13 is an essential mediator of platelet activation in hemostasis and thrombosis. Nat Med 2003; 9:1418-22. [PMID: 14528298 DOI: 10.1038/nm943] [Citation(s) in RCA: 183] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2003] [Accepted: 09/13/2003] [Indexed: 11/09/2022]
Abstract
Platelet activation at sites of vascular injury is essential for primary hemostasis, but also underlies arterial thrombosis leading to myocardial infarction or stroke. Platelet activators such as adenosine diphosphate, thrombin or thromboxane A(2) (TXA(2)) activate receptors that are coupled to heterotrimeric G proteins. Activation of platelets through these receptors involves signaling through G(q), G(i) and G(z) (refs. 4-6). However, the role and relative importance of G(12) and G(13), which are activated by various platelet stimuli, are unclear. Here we show that lack of Galpha(13), but not Galpha(12), severely reduced the potency of thrombin, TXA(2) and collagen to induce platelet shape changes and aggregation in vitro. These defects were accompanied by reduced activation of RhoA and inability to form stable platelet thrombi under high shear stress ex vivo. Galpha(13) deficiency in platelets resulted in a severe defect in primary hemostasis and complete protection against arterial thrombosis in vivo. We conclude that G(13)-mediated signaling processes are required for normal hemostasis and thrombosis and may serve as a new target for antiplatelet drugs.
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Affiliation(s)
- Alexandra Moers
- Institute of Pharmacology, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany
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25
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Manganello JM, Huang JS, Kozasa T, Voyno-Yasenetskaya TA, Le Breton GC. Protein kinase A-mediated phosphorylation of the Galpha13 switch I region alters the Galphabetagamma13-G protein-coupled receptor complex and inhibits Rho activation. J Biol Chem 2003; 278:124-30. [PMID: 12399457 DOI: 10.1074/jbc.m209219200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The present studies mapped the protein kinase A (PKA) phosphorylation site of Galpha(13) and studied the consequences of its phosphorylation. Initial experiments using purified human Galpha(13) and the PKA catalytic subunit established that PKA directly phosphorylates Galpha(13). The location of this phosphorylation site was next investigated with a new synthetic peptide (G(13)SRI(pep)) containing the PKA consensus sequence (Arg-Arg-Pro-Thr(203)) within the switch I region of Galpha(13). G(13)SRI(pep) produced a dose-dependent inhibition of PKA-mediated Galpha(13) phosphorylation. On the other hand, the Thr-phosphorylated derivative of G(13)SRI(pep) possessed no inhibitory activity, suggesting that Galpha(13) Thr(203) may represent the phosphorylation site. Confirmation of this notion was obtained by showing that the Galpha(13)-T203A mutant (in COS-7 cells) could not be phosphorylated by PKA. Additional studies using co-elution affinity chromatography and co-immunoprecipitation demonstrated that Galpha(13) phosphorylation stabilized coupling of Galpha(13) with platelet thromboxane A(2) receptors but destabilized coupling of Galpha(13) to its betagamma subunits. In order to determine the functional consequences of this phosphorylation on Galpha(13) signaling, activation of the Rho pathway was investigated. Specifically, Chinese hamster ovary cells overexpressing human Galpha(13) wild type (Galpha(13)-WT) or Galpha(13)-T203A mutant were generated and assayed for Rho activation. It was found that 8-bromo-cyclic AMP caused a significant decrease (50%; p < 0.002) of Rho activation in Galpha(13) wild type cells but produced no change of basal Rho activation levels in the mutant (p > 0.4). These results therefore suggest that PKA blocks Rho activation by phosphorylation of Galpha(13) Thr(203).
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Affiliation(s)
- Jeanne M Manganello
- Department of Pharmacology, University of Illinois, Chicago, Illinois 60612, USA
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26
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Bodnar RJ, Xi X, Li Z, Berndt MC, Du X. Regulation of glycoprotein Ib-IX-von Willebrand factor interaction by cAMP-dependent protein kinase-mediated phosphorylation at Ser 166 of glycoprotein Ib(beta). J Biol Chem 2002; 277:47080-7. [PMID: 12361948 DOI: 10.1074/jbc.m208329200] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The platelet receptor for von Willebrand factor (VWF), glycoprotein (GP) Ib-IX, mediates initial platelet adhesion and activation. It is known that the cytoplasmic domain of GPIbbeta is phosphorylated at Ser(166) by cAMP-dependent protein kinase (PKA). To understand the physiological role of GPIbbeta phosphorylation, a GPIb-IX mutant replacing Ser(166) of GPIbbeta with alanine (S166A) and a deletion mutant lacking residues 166-181 of GPIbbeta (Delta165) were constructed. These mutants, expressed in Chinese hamster ovary (CHO) cells, showed an enhanced VWF-binding function compared with wild type GPIb-IX. Treatment of CHO cells expressing wild type GPIb-IX with a PKA inhibitor, PKI, reduced Ser(166) phosphorylation and also enhanced VWF binding to GPIb-IX. Furthermore, cells expressing S166A or Delta165 mutants showed a significantly enhanced adhesion to immobilized VWF under flow conditions. Consistent with the studies in CHO cells, treatment of platelets with PKI enhanced VWF binding to platelets. In contrast, a PKA stimulator, forskolin, reduced VWF binding and VWF-induced platelet agglutination, which was reversed by PKI. Thus, PKA-mediated phosphorylation of GPIbbeta at Ser(166) negatively regulates VWF binding to GPIb-IX and is one of the mechanisms by which PKA mediates platelet inhibition.
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Affiliation(s)
- Richard J Bodnar
- Department of Pharmacology, University of Illinois, College of Medicine, Chicago, Illinois 60612, USA
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27
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Yang J, Wu J, Jiang H, Mortensen R, Austin S, Manning DR, Woulfe D, Brass LF. Signaling through Gi family members in platelets. Redundancy and specificity in the regulation of adenylyl cyclase and other effectors. J Biol Chem 2002; 277:46035-42. [PMID: 12297509 DOI: 10.1074/jbc.m208519200] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Platelet responses at sites of vascular injury are regulated by intracellular cAMP levels, which rise rapidly when prostacyclin (PGI(2)) is released from endothelial cells. Platelet agonists such as ADP and epinephrine suppress PGI(2)-stimulated cAMP formation by activating receptors coupled to G(i) family members, four of which are present in platelets. To address questions about the specificity of receptor:G protein coupling, the regulation of cAMP formation in vivo and the contribution of G(i)-mediated pathways that do not involve adenylyl cyclase, we studied platelets from mice that lacked the alpha subunits of one or more of the three most abundantly expressed G(i) family members and compared the results with platelets from mice that lacked the PGI(2) receptor, IP. As reported previously, loss of G(i2)alpha or G(z)alpha inhibited aggregation in response to ADP and epinephrine, respectively, producing defects that could not be reversed by adding an adenylyl cyclase inhibitor. Platelets that lacked both G(i2)alpha and G(z)alpha showed impaired responses to both agonists, but the impairment was no greater than in the individual knockouts. Loss of G(i3)alpha had no effect either alone or in combination with G(z)alpha. Loss of either G(z)alpha or G(i2)alpha impaired the ability of ADP and epinephrine to inhibit PGI(2)-stimulated adenylyl cyclase activity and caused a 40%-50% rise in basal cAMP levels, whereas loss of G(i3)alpha did not. Conversely, deletion of IP abolished responses to PGI(2) and caused cAMP levels to fall by 30%, effects that did not translate into enhanced responsiveness to agonists ex vivo. From these results we conclude that 1) cAMP levels in circulating platelets reflect ongoing signaling through G(i2), G(z), and IP, but not G(i3); 2) platelet epinephrine (alpha(2A)-adrenergic) and ADP (P2Y12) receptors display strong preferences among G(i) family members with little evidence of redundancy; and 3) these receptor preferences do not extend to G(i3). Finally, the failure of ADP and epinephrine to inhibit basal, as opposed to PGI(2)-stimulated, cAMP formation highlights the need during platelet activation for G(i) signaling pathways that involve effectors other than adenylyl cyclase.
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Affiliation(s)
- Jing Yang
- Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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28
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Yamamoto S, Yan F, Zhou H, Tai HH. Agents that elevate cyclic AMP induce receptor phosphorylation primarily at serine 331 in HEK 293 cells overexpressing human thromboxane receptor alpha. Biochem Pharmacol 2002; 64:375-83. [PMID: 12147288 DOI: 10.1016/s0006-2952(02)01053-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Human embryonic kidney (HEK) 293 cells stably transfected with the His-tagged thromboxane receptor alpha (TPalpha) were used to study the phosphorylation and desensitization of the receptor induced by prostaglandin E1 (PGE1) or forskolin. These agents are known to increase the intracellular level of cyclic AMP (cAMP) and activate cAMP-dependent protein kinase (PKA). Pretreatment of cells with either agent significantly attenuated Ca2+ release induced by the agonist [1S-[1alpha,2alpha(Z),3beta(1E,3S),4alpha]]-7-[3-[3-hydroxy-4-(4-indophenoxy)-1-butenyl]-7-oxabicyclo[2,2,1]hept-2-yl]-5-heptenoic acid (I-BOP). These agents also induced concentration-dependent phosphorylation of TPalpha as demonstrated by increased 32P-labeling of the receptor from cells prelabeled with 32P(i). To facilitate the identification of the intracellular domains involved in phosphorylation, glutathione S-transferase (GST)-intracellular domain fusion proteins were used as substrates for purified PKA. It was found that only the C-terminal tail fusion protein could serve as a substrate for PKA. To identify the specific serine/threonine residues in the C-terminal tail that are involved in phosphorylation, various alanine mutants of these residues were checked for their ability to serve as substrates. Ser-331 was found to be involved in PKA-mediated phosphorylation. The S331A mutant receptor overexpressed in HEK 293 cells was not phosphorylated significantly following stimulation by PGE1 or forskolin, indicating that Ser-331 was the major site of phosphorylation. Furthermore, cells overexpressing the mutant receptor became responsive to I-BOP-induced Ca2+ mobilization even after pretreatment with PGE1 or forskolin. These results indicate that Ser-331 is the primary site responsible for the phosphorylation and desensitization of the human TPalpha induced by agents that activate PKA.
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Affiliation(s)
- Shuichi Yamamoto
- Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY 40536-0082, USA
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29
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Gratacap MP, Payrastre B, Nieswandt B, Offermanns S. Differential regulation of Rho and Rac through heterotrimeric G-proteins and cyclic nucleotides. J Biol Chem 2001; 276:47906-13. [PMID: 11560922 DOI: 10.1074/jbc.m104442200] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Platelets were used to study the activation of Rho and Rac through G-protein-coupled receptors and its regulation by cyclic nucleotides. The thromboxane A(2) (TXA(2)) mimetic rapidly activated both small GTPases independently of integrin alpha(IIb)beta(3) activation., which leads to the activation of G(12)/G(13) and G(q) did not induce Rac activation in G alpha(q)-deficient platelets but was able to activate Rho, to stimulate actin polymerization and phosphatidylinositol 4,5-bisphosphate formation, and to induce shape change. Rac activation by in wild-type platelets could be blocked by chelation of intracellular Ca(2+) and was partially sensitive to apyrase and AR-C69931MX, an antagonist of the G(i)-coupled ADP receptor. Cyclic AMP, which completely blocks platelet function, inhibited the -induced activation of G(q) and G(12)/G(13) as well as of Rac and Rho. In contrast, cGMP, which has no effect on platelet shape change blocked only activation of G(q) and Rac. These data demonstrate that Rho and Rac are differentially regulated through heterotrimeric G-proteins. The G(12)/G(13)-mediated Rho activation is involved in the shape change response, whereas Rac is activated through G(q) and is not required for shape change. Cyclic AMP and cGMP differentially interfere with -induced Rho and Rac activation at least in part by selective effects on the regulation of individual G-proteins through the TXA(2) receptor.
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Affiliation(s)
- M P Gratacap
- Pharmakologisches Institut, Universität Heidelberg, Im Neuenheimer Feld 366, Heidelberg 69120, Germany
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30
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Abstract
Cardiovascular diseases are often accompanied and aggravated by pathologic platelet activation. Tight regulation of platelet function is an essential prerequisite for intact vessel physiology or effective cardiovascular therapy. Physiological platelet antagonists as well as various pharmacological vasodilators inhibit platelet function by activating adenylyl and guanylyl cyclases and increasing intracellular cyclic AMP (cAMP) and cyclic GMP (cGMP) levels, respectively. Elevation of platelet cyclic nucleotides interferes with basically all known platelet activatory signaling pathways, and effectively blocks complex intracellular signaling networks, cytoskeletal rearrangements, fibrinogen receptor activation, degranulation, and expression of pro-inflammatory signaling molecules. The major target molecules of cyclic nucleotides in platelets are cyclic nucleotide-dependent protein kinases that mediate their effects through phosphorylation of specific substrates. They directly affect receptor/G-protein activation and interfere with a variety of signal transduction pathways, including the phospholipase C, protein kinase C, and mitogen-activated protein kinase pathways. Regulation of these pathways blocks several steps of cytosolic Ca(2+) elevation and controls a multitude of cytoskeleton-associated proteins that are directly involved in organization of the platelet cytoskeleton. Due to their multiple sites of action and strong inhibitory potencies, cyclic nucleotides and their regulatory pathways are of particular interest for developing new approaches for the treatment of thrombotic and cardiovascular disorders.
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Affiliation(s)
- U R Schwarz
- Institut für Klinische Biochemie und Pathobiochemie, Medizinische Universitätsklinik, Josef-Schneider Str. 2, 97080, Würzburg, Germany
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31
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Foley JF, Kelley LP, Kinsella BT. Prostaglandin D(2) receptor-mediated desensitization of the alpha isoform of the human thromboxane A(2) receptor. Biochem Pharmacol 2001; 62:229-39. [PMID: 11389883 DOI: 10.1016/s0006-2952(01)00661-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Thromboxane (TX) A(2) and prostaglandin (PG) D(2) mediate opposing actions in platelets and in vascular and non-vascular smooth muscle. Here, we investigated the effects of stimulation of the PGD(2) receptor (DP) on signaling by the TXA(2) receptor (TP) expressed in human platelets and in human embryonic kidney (HEK) 293 cells over-expressing the individual TP alpha and TP beta isoforms. In platelets, the selective DP agonist BW245C abolished TP-mediated mobilization of intracellular calcium ([Ca(2+)](i)) and inhibited platelet aggregation in response to the TXA(2) mimetic U46619. DP-mediated desensitization of TP signaling in platelets was prevented by pretreatment with the cAMP-dependent PKA inhibitor, H-89, but was unaffected by the PKC inhibitor GF 109203X. In HEK 293 cells, signaling by TP alpha, but not TP beta, was subject to DP-mediated desensitization in a PKA-dependent, PKC-independent manner. U46619-induced signaling by TP(Delta 328), a truncated variant of TP containing only those residues common to TP alpha and TP beta, was insensitive to prior DP stimulation, indicating that the carboxyl terminal tail of TPalpha contains the target site(s) for DP-mediated desensitization. Mutation of Ser(329) to Ala(329) within a consensus PKA site in TP alpha rendered the mutant TP alpha(S329A) insensitive to BW245C-mediated desensitization. Whole cell phosphorylation assays established that TP alpha, but not TP beta or TP alpha(S329A), was subject to DP-mediated phosphorylation and that TP alpha phosphorylation was blocked by the PKA inhibitor H-89. These data establish that TP alpha, but not TP beta, is subject to DP-mediated cross desensitization, which occurs through direct PKA-mediated phosphorylation of TP alpha at Ser(329).
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MESH Headings
- 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid/pharmacology
- Blood Platelets/drug effects
- Blood Platelets/metabolism
- Cells, Cultured
- Humans
- Hydantoins/pharmacology
- Inositol 1,4,5-Trisphosphate/metabolism
- Phosphorylation
- Protein Isoforms/physiology
- Receptor Cross-Talk/physiology
- Receptors, Immunologic
- Receptors, Prostaglandin/antagonists & inhibitors
- Receptors, Prostaglandin/metabolism
- Receptors, Prostaglandin/physiology
- Receptors, Thromboxane/physiology
- Signal Transduction
- Vasoconstrictor Agents/pharmacology
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Affiliation(s)
- J F Foley
- Department of Biochemistry, Conway Institute of Biomolecular and Biomedical Research, Merville House, University College Dublin, Belfield, Dublin 4, Ireland
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Dunlop PC, Leis LA, Johnson GJ. Epinephrine correction of impaired platelet thromboxane receptor signaling. Am J Physiol Cell Physiol 2000; 279:C1760-71. [PMID: 11078690 DOI: 10.1152/ajpcell.2000.279.6.c1760] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study evaluated the mechanism of epinephrine potentiation of platelet secretion induced by thromboxane A(2) (TXA(2)). Dog platelets that do not secrete in response to TXA(2) alone (TXA(2)-) were compared with dog platelets that do secrete (TXA(2)+) and with human platelets. TXA(2)- platelets had impaired TXA(2) receptor (TP receptor)-G protein coupling, indicated by 1) impaired stimulated GTPase activity, 2) elevated basal guanosine 5'-O-(3-thiotriphosphate) binding, and 3) elevated Galpha(q) palmitate turnover that was corrected by preexposure to epinephrine. Kinetic agonist binding studies revealed biphasic dog and human platelet TP receptor association and dissociation. TXA(2)- and TP receptor-desensitized TXA(2)+ dog and human platelets had altered ligand binding parameters compared with untreated TXA(2)+ or human platelets. These parameters were reversed, along with impaired secretion, by epinephrine. Basal phosphorylation of TXA(2)- platelet TP receptors was elevated 60% and was normalized by epinephrine. Epinephrine potentiates platelet secretion stimulated by TXA(2) by reducing basal TP receptor phosphorylation and facilitating TP receptor-G protein coupling in TXA(2)- platelets and, probably, in normal platelets as well.
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Affiliation(s)
- P C Dunlop
- Hematology/Oncology Section, Department of Medicine, Veterans Administration Medical Center and University of Minnesota, Minneapolis, Minnesota 55417, USA
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Walsh MT, Kinsella BT. Regulation of the human prostanoid TPalpha and TPbeta receptor isoforms mediated through activation of the EP(1) and IP receptors. Br J Pharmacol 2000; 131:601-9. [PMID: 11015313 PMCID: PMC1572368 DOI: 10.1038/sj.bjp.0703624] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The intermolecular cross-regulation mediated by the prostanoid IP-receptor (IP)/EP(1) receptor (EP(1)) agonists PGI(2) and 17 phenyl trinor PGE(2) on TP receptor (TP) signalling within platelets was compared to that which occurs to the individual TPalpha and TPbeta receptors over-expressed in human embryonic kidney (HEK) 293 cells. Ligand mediated TP receptor activation was monitored by analysing mobilization of intracellular calcium ([Ca(2+)](i)) following stimulation with the selective thromboxane (TX) A(2) mimetic U46619. Consistent with previous studies, in platelets, PGI(2) acting through endogenous IP receptors completely inhibited U46619-mediated TP receptor signalling in a protein kinase (PK) A-dependent, PKC-independent manner. In HEK 293 cells, PGI(2), acting through endogenous AH6809 sensitive EP(1) rather than IP receptors, and the selective EP(1) receptor agonist 17 phenyl trinor PGE(2) antagonized U46619-mediated signalling by both TPalpha and TPbeta receptors in a PKC-dependent, PKA-independent manner. The maximum response induced by either ligand was significantly (P<0.005) greater for the TPalpha receptor than the TPbeta receptor, pointing to possible physiologic differences between the TP isoforms, although the potency of each ligand was similar for both TP receptors. TP(Delta328), a truncated variant of TP receptor lacking the C-tail sequences unique to TPalpha or TPbeta receptors, was not sensitive to EP(1) receptor-mediated regulation by PGI(2) or 17 phenyl trinor PGE(2) In conclusion, these data confirm that TPalpha and TPbeta receptors are subject to cross regulation by EP(1) receptor signalling in HEK 293 cells mediated by PKC at sites unique to the individual TP receptors and that TPalpha receptor responses are significantly more reduced by EP(1) receptor regulation than those of the TPbeta receptor.
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MESH Headings
- 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid/pharmacology
- Biological Transport/drug effects
- Blood Platelets/drug effects
- Blood Platelets/metabolism
- Calcium/metabolism
- Cells, Cultured
- Dinoprostone/pharmacology
- Drug Interactions
- Enzyme Inhibitors/pharmacology
- Epoprostenol/pharmacology
- Humans
- Indoles/pharmacology
- Isoquinolines/pharmacology
- Maleimides/pharmacology
- Prostaglandin Antagonists/pharmacology
- Prostaglandins/metabolism
- Protein Isoforms/metabolism
- Receptors, Epoprostenol
- Receptors, Prostaglandin/metabolism
- Receptors, Prostaglandin E/metabolism
- Receptors, Prostaglandin E, EP1 Subtype
- Receptors, Thromboxane/antagonists & inhibitors
- Receptors, Thromboxane/metabolism
- Signal Transduction
- Sulfonamides
- Vasoconstrictor Agents/pharmacology
- Xanthenes/pharmacology
- Xanthones
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Affiliation(s)
- Marie-Therese Walsh
- Department of Biochemistry, Conway Institute of Biomolecular and Biomedical Research, Merville House, University College Dublin, Belfield, Dublin 4, Ireland
| | - B Therese Kinsella
- Department of Biochemistry, Conway Institute of Biomolecular and Biomedical Research, Merville House, University College Dublin, Belfield, Dublin 4, Ireland
- Author for correspondence:
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Affiliation(s)
- P V Halushka
- Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Department of Medicine, Division of Clinical Pharmacology, Medical University of South Carolina, 171 Ashley Ave., Charleston, SC 29425, USA.
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